BARCELONA, SPAIN — Streptococcus pneumoniae, the bacteria that causes pneumococcal disease, is sixfold more likely to colonize adults older than 60 years who have regular contact with children than those who do not, data from a community-based study showed.
However, there is “no clear evidence of adult-to-adult transmission,” and the researchers, led by Anne Wyllie, PhD, from the Yale School of Public Health, New Haven, Connecticut, noted that the study results suggest “the main benefit of adult pneumococcal conjugate vaccine (PCV) immunization is to directly protect adults who are exposed to children, who still carry and transmit some vaccine-type pneumococci despite successful pediatric national immunization programs.”
The data show that relatively high pneumococcus carriage rates are seen in people who have regular contact with children, who have had contact in the previous 2 weeks, and who have had contact for extended periods, Wyllie explained.
Preschoolers in particular were found to be most likely to transmit pneumococcus to older adults. “It is the 24- to 59-month-olds who are most associated with pneumococcal carriage, more than 1- to 2-year-olds,” she reported. However, transmission rates from children younger than 1 year are higher than those from children aged 1-2 years, she added.
The findings were presented at the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) 2024 global conference, formally known as the ECCMID conference.
Originally Designed to Investigate Adult-to-Adult Transmission
The researchers wanted to understand the sources and dynamics of transmission, as well as the risk factors for pneumococcal disease in older adults, to help predict the effect of PCVs in people older than 60 years.
Although “we designed the study to specifically look at transmission between adults, in the end, we were presented with a very unique scenario” — restricted social mixing as a result of the COVID pandemic — during which “no community activities were happening,” Wyllie said. Because of this, the team was able to determine “the source of acquisition or transmission to the older adults was, very likely, coming from contact with children.”
Pneumococci are commonly found in respiratory tracts of healthy people. The US Centers for Disease Control and Prevention estimated that 20%-60% of school-aged children may be colonized compared with only 5%-10% of adults without children.
The longitudinal study was conducted among household pairs, such as married couples who were both aged at least 60 years and who did not have people younger than 60 years living in the household, in New Haven over two winter seasons: 2020-2021 and 2021-2022.
Self-collected saliva samples were assessed, and surveys on social behaviors and health were completed every 2 weeks for a 10-week period (with six study visits). The saliva sampling method was used because the researchers considered it to be more effective than samples from nasopharyngeal swabs. Quantitative polymerase chain reaction assays were used to test the saliva samples for the presence of pneumococcal DNA (pneumococcus genes piaB and lytA) and the diversity of pneumococcal strains (36 serotypes were targeted).
Strongly Suggestive of Transmission From Kids to Older Adults
Of the 121 adults living in 61 households who were enrolled in the study, 62 adults participated in both seasons. Mean age was 70.9 years (range, 60-86 years), 51% of participants were women, and 85% were White.
Overall, 52 of 1088 (4.8%) samples tested positive for pneumococcus, and 27 of 121 (22.3%) adults were colonized on at least one sampling visit. Some were colonized at multiple timepoints, and two were colonized throughout the 10-week sampling period. Of the two participants who were colonized at five of six timepoints, one reported daily contact with children younger than 5 years and children aged 5-9 years in the two study seasons. This person was also positive at three of six sampling points during the first study season.
There were five instances in which both members of the household were carriers in the same season, although not necessarily at the same timepoint. Numbers were too small to determine whether transmission had occurred between the household pairs.
Contact with a 24- to 59-month-old child (older than 2 years but younger than 5 years) had the strongest association with elevated odds of carrying pneumococcus, the authors reported in their preprint, although the frequency and intensity of contact also mattered.
At any sampled time (point prevalence), pneumococcal carriage was substantially — just over sixfold — higher among older adults who had contact with children daily or every few days (10%) than among those who had no contact with children (1.6%).
In particular, contact between adults and children younger than 5 years and children aged 5-9 years was found to lead to elevated point prevalences of 13.8% and 14.1%, respectively. Pneumococcal carriage in children older than 10 years was lower, with a point prevalence of 8.3%.
The younger the child, the greater the point prevalence; point prevalences were 13.8% for samples from children aged 1 year and younger, 10.5% for samples from children aged 1-2 years, and 17.8% for children aged 2-5 years.
Carriage prevalence was higher in older adults who reported daily contact with children (15.7%) or contact every few days (14.0%) than in those who reported contact with children only once or twice a month (4.5%) or never (1.8%), they wrote.
“Older people who have a lot of contact with kids and are more susceptible to respiratory viruses can get a secondary infection from pneumococcus, especially during the cold and flu seasons. Vaccination can help to protect them or lessen severity of the illness,” Wyllie pointed out.
However, adult PCV immunization may not have a major impact on onward transmission to other adults, the authors wrote in their preprint.
This study supports prior work demonstrating that pneumococcal colonization is greater in households with children than in those without, said Stephen Pelton, MD, a pediatric infectious disease specialist from Boston University Schools of Medicine and Public Health, Boston. “The unique aspect is that Dr Wyllie’s group has looked at individuals over age 60 and used the most sensitive methods currently available to detect pneumococcal carriage.”
“At the most recent ISPPD [International Society of Pneumonia and Pneumococcal Diseases conference], the role of adult-to-adult transmission in the community was discussed. This study confirms the critical role children play in community transmission of the pneumococcus,” Pelton noted.
Wyllie received consulting and/or advisory board fees from Pfizer, Merck, Diasorin, PPS Health, Primary Health, Co-Diagnostics, and Global Diagnostic Systems for work unrelated to this project and is the principal investigator on research grants from Pfizer, Merck, NIH RADx-UP, and SalivaDirect, Inc. to Yale University and from NIH RADx, Balvi.io, and Shield T3 to SalivaDirect, Inc. Pelton received honoraria from Merck, Pfizer, Sanofi, and GSK for participation in Pneumococcal Advisory Boards and DSMB (Sanofi). Boston Medical Center received grant funding for investigator-initiated research from Merck and Pfizer.